Laminar flow fans are commonly used for impelling a fluid medium (a liquid or gas). In particular, they are suited to low flow, high back pressure forced air;cooling of electrical apparatus when low acoustic fan noise is required. Typically, these fans comprised an assembly of parallel annular or frustro-conical elements, mounted in spaced apart relationship and face-to-face about a common rotation axis. In operation, the assembly is rotated about this axis by a suitable motor; the fluid is drawn in at the center of the assembly, impelled towards the outer edges of the elements by viscous interaction with the surface of the elements and, is finally expelled at the periphery of the assembly. Examples of laminar flow fans may be found in GB 2 126 653 and U.S. Pat. No. 2,632,598.
A large variety:of cooling systems have been proposed for providing efficient cooling of a number of electrical or electronic devices housed together in an enclosure. In many of today's computer system units, a number of different elements including mass storage devices, circuit cards and associated power supplies are provided which must be cooled sufficiently in order to ensure safe operating temperatures. The cooling system employed in such system units commonly comprises one or more axial flow fans placed at the rear of the unit which operate to draw cooling air through apertures in the front bezel of the unit, over the electrical devices and to expel exhaust air through apertures at the rear of the unit. One common type of system unit is the floor standing `tower` in which a tower is supported in an upright position by a support foot.
While these cooling systems are undoubtedly adequate for the purpose, they have a number of drawbacks. Firstly, the fan take up valuable space within the unit which results in an increase in the overall size of the unit and secondly the noise produced by axial fans can be significant in an office environment.